The present invention relates generally to a process for finishing the surfaces of plastics, being particularly suitable for surface finishing or polishing plastic components having shapes that are difficult to treat, such as those of small tubes and those including internal curves. In an especially preferred application, generally tubular components of medical equipment such as blood processing systems are polished to prevent hemolysis of blood when flowing therethrough, such components advantageously being made of inert or insoluble plastics.
Processes for finishing generally soluble plastics with solvent vapors are known. Representative of such known processes is Van Dyk U.S. Pat. No. 3,684,553, which discusses various surface treatments of thermoplastic polymer articles with a solvent for the thermoplastic polymer. These processes take advantage of the physical properties of the polymer, including its ability to be softened but not deformed by moderate heat and its ability to be readily dissolved by a solvent, which physical properties will allow the surface thermoplastic polymer to soften, flow and thereafter cool to reharden the surface of the article to an improved smoothness developed when surface defects on the article were generally liquified.
In proceeding in accordance with such known processes, the plastic article being treated is made of a material that is readily solventized by the solvent being used to treat the article. Certain plastic articles, for example medical equipment components that come into contact with body fluids such as blood and the like to be used in treating people, are most desirably made of insoluble and substantially inert polymers which are especially resistant to chemical breakdown and deterioration in general which would result in the transfer of polymer or polymer constituents into the body fluid contacted thereby or flowing therethrough during use of the medical equipment.
Heretofore, these highly desirable types of insoluble plastic materials could not be successfully used in manufacturing component parts that are particularly small or have difficult to reach surfaces making them extremely difficult, if not impossible, to be mechanically polished to the degree necessary for satisfactory elimination of surface defects, the minimization or elimination of such surface defects being particularly important for component parts that contact body fluids, especially when the body fluids flow through or otherwise impinge upon a surface having irregularity defects. One particularly difficult problem arises in attempting to take advantage of the beneficial medical attributes of the very insoluble inert plastic materials such as polymethylpentene and polypropylene by using these materials to make component parts, particularly the tubular and the small irregularly shaped component parts within blood processing systems, which use is severely hampered by the polishing barriers that were heretofore encountered in attempting to remove surface irregularities from inert components of this type, most critically those surface irregularities that can often lead to hemolysis of blood flowing through or impinging upon such component parts.
By proceeding in accordance with the process of the present invention, it is possible to treat component parts made of insoluble or inert plastics through the action of a fluid medium thereon, which fluid medium is brought into contact with remote areas of the component part to form surface finishes that are extremely smooth and free from minor variations such as machining marks, defects developed during molding procedures, handling damage, and damage from secondary operations such as sprue removal. These operations can be carried out on a large-scale commercial basis without requiring intricate hand polishing of individual component parts, the process of this invention making it possible to treat an insoluble plastic component part with a fluid medium which would not otherwise solubilize the surface of the plastic part without subjecting that part to a temperature at which the insoluble plastic component part would deform.
In an important aspect of the present invention, a positive pressure is applied within the environment of the part being treated in order to improve the distribution of the medium on, throughout and into the component part being polished. This effect is further improved when the pressurized vapor is vented from the treatment vessel in order to enhance the flow of the vaporized treatment fluid over and through the component part.
These aspects and advantages of the present invention are brought about by a process which includes preheating the insoluble plastic component part to well below its softening or deformation temperature and contacting it with a vaporized fluid medium which is not a solvent for the inert or insoluble plastic material at the treatment temperature but which would be a solvent for the inert material at a temperature which would result in deformation of the plastic component part. More particularly, the preheated part and the vaporized fluid medium are brought into contact within a pressure vessel, and held therein while pressures are developed primarily through the action of the heated vapor as it expands through a phase change within a pressurized vessel. The pressure may be increased further and the fluid medium made more dense by mechanically applying a supplemental positive pressure to the vaporized fluid medium within the pressure chamber.
It is accordingly a general object of the present invention to treat the surface of insoluble plastics.
Another object of the present invention is an improved process for surface finishing plastic articles by an improved process using a fluid medium in which the plastic is insoluble at atmospheric pressure unless the plastic were to be raised to a temperature at which it would deform.
Another object of the present invention is an improved process for melting the surface of an insoluble or inert plastic component and then allowing the surface to reform from this molten state in order to produce a finish that is extremely smooth and free from minor surface variations such as machining marks, molding burrs, handling damage and defects which develop upon use.
Another object of the present invention is an improved process for surface finishing articles made of insoluble plastic by applying a slight positive pressure for increasing the density of the treatment fluid to thereby enhance the circulation thereof to all surfaces of the part.
Another object of this invention is a means for providing highly polished medical equipment components having surfaces to which access is difficult to obtain.